Material tester



Dec. 16, 1969 w. R. APPLE ETAL 3,483,721

MATERIAL TESTER Filed Dec. 30, 1966 Fig. l.

WAYNE R. APPLE DALE A. MALE) 28 /268 40 264 INVENTORS Z4 26 I I 5% 7? ATTORNEY United States Patent Office 3,483,721 Patented Dec. 16, 1969 3,483,721 MATERIAL TESTER Wayne R. Apple and Dale R. Maley, Boulder, Colo., as-

signors to Automation Industries, Inc., El Segundo, Calif, a corporation of California Filed Dec. 30, 1966, Ser. No. 606,392

Int. Cl. B21b 37/10 US. Cl. 7213 12 Claims ABSTRACT OF THE DISCLOSURE An inspection station in a rolling mill for detecting laminar defects in plate is disclosed. The hot plate is passed over a cooling jet, and then is scanned by a radiometer. Temperature differentials caused by the defects are sensed by the radiometer. Suitable indicating or alarm means, connected to the radiometer, are triggered by the differing temperatures.

The present invention relates to the manufacture of rolled steel stock, such as sheets and plates and more particularly to means for insuring the stock is rolled free from any internal defects. In one steel manufacturing process a hot bloom or billet is rolled into thinner stock, such as a sheet or plate. When the stock has a thickness on the order of about one-fourth inch or less it is normally referred to as a sheet, whereas if the thickness is in the general range of about one-fourth inch up to an inch or more it is normally referred to as plate. The width of the rolled stock may be on the order of up to 90 or 100 inches or more while the length may be up to 20 or 30 feet or more. After the sheets or plates are rolled to the required thickness they are trimmed to the desired dimensions, sorted and allowed to cool to ambient temperature. Subsequently they may be fabricated into more complex structures by cold rolling into thin sheets, cutting, bending etc.

Under some circumstances certain types of laminar defects, such as edge laminations and pipe inclusions may develop in the stock as it is being rolled. Both types of defects are approximately midway between the top and bottom surfaces and are not visible to the naked eye or at least are extremely difficult to detect by visual inspection. Edge laminations are normally close to one edge of the stock and are probably formed by the deformations of the stock produced by the original rolling operation. Pipe inclusions are normally near the centerline of the stock and are usually caused by inclusions such as slag or air bubbles etc. cast into the original ingot. If the rolled stock contains defects of the foregoing variety during further processing, such as stamping, bending, cutting, welding or even further rolling etc., the defects tend to grow and/or eventually produce a costly failure. It is, therefore, highly desirable to locate any defects in the rolled stock as early as possible and preferably during or immediately following the rolling operations. The sooner a defect is located the less the investment in time and materials and the greater the possiblity of salvage.

Heretofore numerous test systems, such as ultrasonic, dye penetrants, magnetic, eddy current etc. have been proposed for inspecting the plates. These systems have been successful to some extent in detecting some types of defects but not necessarily the laminar type of defect most common in steel plates. Moreover they have all required a pickup probe or search unit that must be in direct physical contact with the plate or else must be extremely close thereto. The surface temperature during the rolling operation and immediately thereafter is normally too high to permit inspecting it by any means which must contact the surface. Accordingly heretofore it has been necessary to complete the rolling operation and allow the plate to cool to ambient temperature before it could be inspected. This, of course, is a time consuming operation and normally delays inspection until after the rolling and final trimming or cropping operations. As a consequence, in the the event a defect were located it was usually no longer possible to salvage the plate by judious cropping etc. Also, if additional rolling etc. were required it was necessary to reheat the plate. It may thus be seen that the prior plate rolling processes have not been entirely satisfactory for all purposes.

It is not proposed to provide means for overcoming the foregoing difficulties. More particularly it is proposed to provide a rolling mill having means therein for locating internal defects in the stock while the stock is being rolled or immediately thereafter. It is also proposed to provide means for locating defects prior to the time the plate is trimmed or cropped to its final dimensions. As a consequence if a defect is present any desirable corrective action may be taken during the rolling operation or before the plate has cooled. Also, additional and Wasted processing maybe eliminated if the defect cannot be corrected.

In the single embodiment of the invention disclosed herein this is accomplished by providing a rolling mill having an infrared inspection station adjacent to the rolling station and prior to the cropping station. The infrared inspection station is effective to scan the plate during or immediately following the rolling operation and thereby sense the changes in surface temperatures occuring during or following the rolling operation. If any defects, such as edge laminations or pipe inclusions are present in the plate there will be corresponding variations in the surface temperatures and the defects will be located.

These and other features and advantages of the present invention will become readily apparent from the following detailed description of a single embodiment thereof, particularly when taken in connection with the accompanying drawings wherein like reference numerals refer to like parts and wherein;

FIGURE 1 is a side view of a portion of a rolling mill embodying the present invention;

FIGURE 2 is a perspective view of an infrared inspection station contained Within the rolling mill of FIGURE 1; and

FIGURES 3 and 3A are a plan view and an end View, respectively, of rolled stock containing typical types of laminar defects.

Referring to the drawings in more detail the present invention is particularly adapted to be embodied in a system 10 for rolling blooms into steel sheets or plates. This system 10 includes a rolling station 12, a trimming or cropping station 14, a rolling table 16 extending therebetween and an inspection station 18 disposed on said rolling table 16 between the rolling station 12 and the the cropping station 14.

The rolling station 12 includes a pair of enlarged rollers 20 adapted to receive a billet or bloom from the blooming mill. These rollers 20 are effective to compress or roll the billet or bloom into rolled stock 22 having a substantially uniform thickness.

The rollers 20 are normally about 2 to 3 feet in diameter and may be on the order of up to 5 or 10 feet long whereby the finished stock 22 may have a corresponding width. The lengths of the fully rolled stock 22 vary over a considerable range and are frequently on the order of up to about 20 or 30 feet long. If the stock 22 is rolled to a thickness on the order of about 0.060" to about 0.250" it is normally referred to as sheet. Whereas, if it is rolled to a thickness in a range from about up to about 1 /4 or more it is usually referred to as plate.

Prior to, during and following the rolling operation the stock has an elevated temperature which, under some circumstances, may be in the red hot region. The stock 22 is normally hot worked during the rolling operation and the surface temperature remains in an elevated region. In a typical rolling mill the temperature of the fully rolled stock 22 as it leaves the last set of rollers is frequently in the region of about 1800 Fahrenheit. However, in some mills it may be anywhere from about 1000 to about 2000 Fahrenheit.

If there are any inclusions such as slag, clay, sand, air bubbles etc. present in the ingot when it is cast, they tend to remain in that portion of the ingot which is still in the liquid phase. Since the center of the ingot is the last to solidify many of the inclusions are at or near the center of the ingot. As a consequence as the bloom and rolled stock 22 ar formed the inclusions tend to remain concealed below the surface and are extremely difficult, if not impossible, to visually observe. Typically in the fully rolled stock 22 the inclusions are normally centered approximately midway between the top and bottom surfaces of the stock 22 and somewhere around the longitudinal centerline thereof, as seen in FIGURE 3. Moreover, the inclusions are frequently located very near to one end of the stock.

During the rolling of the stock 22 its thickness is decreased and the material spread over a wider area. At the same time any inclusions are also rolled flat and spread. As a consequence an inclusion of this type may expand to cover several square feet by the time the stock 22 is fully rolled. As previously stated, the inclusions 24 are normally located approximately midway between the top and bottom of the stock 22, around the centerline and near one end similar to the one in FIGURE 3. Since this tends to produce hollow stock 22 this type of defect is frequently called a pipe inclusion.

Under some circumstances a small crack or inclusion may be present in the stock 22 immediately adjacent to the edge 28 thereof. This may cause the edge of the stock 22 to begin to develop a laminar separation. Since these separations are normally at or near the edge 28 they are frequently referred to as edge laminations. During the repeated rolling and working this separation 26 gradually grows inwardly from the edge 28 of the plate and may also eventually cover up to several square feet. Edge laminations may be at or near one end of the plate as at 26A or near the middle as at 26B.

The rolling table 16 is disposed adjacent to th rollers 20 and receives the fully rolled stock 22 as it emerges from the rollers 20. This table 16 includes a plurality of substantially parallel and horizontal side rails 30 with several relatively small diameter rollers 32 extending therebetween. These rollers 32 are adapted to support the weight of the stock 22 and allow it to be moved longitudinally on the table. Normally at least a portion of the rollers 32 are power driven whereby the operator can control the longitudinal position of the stock 22 on the table 16 and can even cause it to be repeatedly passed back and forth through th rollers 20 until it is rolled down to the desired thickness.

The cropping or trimming station 14 is disposed adjacent the end of the rolling table 16. After the stock 22 has been passed through the rollers 20 and reduced in thickness to the desired level, the rollers 32 are driven to carry the stock 22 through the trimming station 14. At this point the ends and/or edges of the stock 22 are trimmed or cropped to reduce the stock 22 down to the desired Width or length. Also, if there are any defects present in the stock 22 the defective portions may be cropped. This removes the defect and leaves entirely sound rolled stock. Sinc the stock 22 is still very hot at this time these trimming or cropping operations may be easily performed. Following the trimming or cropping operation the stock 22 is sorted according to its intended future use, shunted into a storage area and allowed to cool to ambient temperature.

In order to locate the various defects, such as pipe inclusions 24, edge laminations 26 etc. the inspection station 18 may scan the plate 22 as it travels across the rolling table 16. This inspection may occur between successive rolling operations. However, in the present instance it is made after the rolling is completed and the stock 22 is ready to be transferred to the cropping station 14.

The present inspection station .18 is of the so-called infrared variety wherein the radiations from the stock 22 are monitored. As a result the station 18 may be effectively separated by a considerable distance from the stock 22 and thereby protected from extremely high surface temperatures on the rolled stock 22. The station 18 includes means such as a radiometer 34 for receiving the infrared radiations and producing an electrical signal corresponding thereto.

The radiometer 34 includes an optical head 38 having an infrared cell or similar device responsive to the magnitude of the radiations in the wavelength of the energy being radiated from the surface 40 of the rolled stock 22. The cell is effective to produce an electrical signal that is a function of these radiations. A lens system 42 is focused onto a relatively small scan spot 36 on the surface 40 of the rolled stock 22 to concentrate these radiations on the cell. A signal will thereby be produced from the optical head 38 which is a function of the surface temperature at the scan spot 36.

The'output from optical head 38 is coupled to suitable electronics 44 such as an amplifier etc. for processing the temperature signal. Output means such as an alarm 46 and/or meter 48 to indicate when the temperature is outside of a particular range and/or to indicate the temperature at the scan spot 36.

As the stock 22 is rolled to its final dimensions and carried across the table 16 it begins to cool. Because of convection cooling and for other reasons the heat losses from the top surface 40 of the rolled stock 22 are on the order of double the losses in a downward direction from the bottom surface 50. As a consequence the top surface 40 is normally considerably hotter than the bottom surface 50 and there is a generally upward flow of thermal energy through the stock 22.

It can be appreciated if there are any discontinuities in the thermal conductivity of the stock 22 there will be corresponding variations in the rate at which the energy flows upwardly. These in turn will produce corresponding localized variations in the surface temperature. As the radiometer 34 scans the surface 40 of the rolled stock 22 it will produce fluctuations in the temperature signal corresponding to the localized variations in the surface temperature.

It has been found the temperature differences occurring around defects tend to be of relatively small magnitude if the stock is merely allowed to cool naturally. As a consequence the radiometer 34 must be quite sensitive to detect these variations and produce a signal having a satisfactory signal-to-noise ratio. It has been found the temperature variations can be increased if the cooling rate is increased and particularly if the increased cooling occurs on only one side of the stock 22. If this cooling is of sufficient magnitude there will be a very large difference between the temperatures on the top and bottom surfaces 40 and 50. The thermal energy will thereby flow downwardly from a region just below the top surface 40 toward the bottom surface 50. As a consequence the flow of thermal energy will be substantially entirely downwardly. If the rolled stock 22 has a uniform thermal conductivity the temperature of the top surface 40 will be uniform. However, if there is a discontinuity such as an inclusion 24 or lamination 26 there will be a corresponding discontinuity in the thermal conductivity. This, in turn, will result in a variation in the temperature of the upper surface 40.

In order to produce the foregoing type of accelerated Cooling, s g d v c su h a a j t may b p qviqed;

below the rolled stock 22 in the region where it leaves the rollers 20. This jet 52 may direct a stream 54 of coolant such as cold air, water, etc. against the bottom 50 of the stock 22. This coolant will absorb large quantities of thermal energy and lower the bottom surface 50 temperature. The optical system 42 for the radiometer 34 is focused on a scan spot 36. This spot 36 is spaced at considerable distance, for example several feet, away from the area cooled by the jet 52. By the time the rolled stock 22 has traveled over this distance a large quantity of thermal energy has flowed downwardly toward the bottom surface 50 and the temperature of the top surface 40 has been greatly reduced. The radiometer 34 will thereby produce a signal that is a function of this reduced temperature.

As explained above the temperature of the upper surface 40 at this scan spot 36 is a function of the thermal conductivity of the rolled stock 22. If the stock 22 is uniform the conductivity is uniform and the temperature is constant. However, if there is a discontinuity such as an inclusion 24 of lamination 26 there will be a variation in the temperature of the scan spot 36 as this portion moves past the scan spot 36.

In order to utilize this system the unrolled material is fed between the two rolls 20 and onto the table 16. As the rolled stock 22 enters the inspection station 18 the jet 52 directs a stream 54 of coolant against the underside 50 of the hot stock 22. This coolant absorbs large quantities of thermal energy from the stock 22. Thermal energy then flows downwardly from the region of the upper surface 40 toward the bottom surface 50. This, in turn, produces an accelerated cooling of the top surface 40 as it moves toward the scan spot 36. The radiometer 34 receives the radiations from this spot 36 and produces a temperature signal. The temperature of the top surface 40 will normally be reduced by a fixed amount when it reaches the scan spot 36 and the temperature signal will be constant.

However if there is a discontinuity such as a pipe inclusion 24 or lamination 26 there is a corresponding localized variation in the thermal conductivity. Normally this is a decrease in the conductivity whereby the rate of heat transfer is decreased. This in turn prevents the temperature of surface 40 decreasing as rapidly whereby a hot spot is produced in the region of the discontinuity. As the scan spot 36 travels over this hot spot the signal from the radiometer 34 increases whereby the alarm 46 or meter 48 will indicate a defect.

It has been found the pipe inclusions 24 are normally disposed on the center line of the stock 22. Accordingly if a single cooling jet 52 is provided at the center line of the stock and the lens system 42 is focused on the center line, the scan spot 36 will follow a straight scan line which passes over this type of defect.

It has also been found edge laminations 26 are located adjacent to the edges 28. Accordingly, if a pair of cooling jets are directed toward the regions of the stock adjacent the edges and a pair of radiometers are focused on the same regions these edge laminations will be detected. It can be seen three fixed radiometers may be focused to scan along three laterally spaced lines positioned to locate the inclusions and edge laminations.

If it is desired to scan the entire stock 22 it has been found advantageous to use a single radiometer 34. This radiometer 34 may then be oscillated to move the scan spot 36 transversely of the stock. This will cause the entire surface 40 of the stock 22 to be scanned along a generally zig-zag scan path 56. If this type of scanning is to be employed it has been found advantageous to utilize a broad cooling jet 52'. This jet 52 directs a sheet of coolant against the under surface so as to cool the entire surface.

As the rolled stock 22 moves through the inspection station 18 all defects such as the edge laminations 26 and pipe inclusions 24 will be identified. Accordingly when the stock 22 reaches the cropping station 14 the defective portions may be removed whereby only sound material remains.

While only a single embodiment of the present invention is disclosed herein, it will be readily apparent to persons skilled in the art that numerous changes and modifications may be made thereto without departing from the scope of the invention. For example, it has been found that directing large quantities of coolant, such as cold water, against very hot stock may have an adverse effect on the stock. More particularly it may cause warping, twisting etc. To avoid this condition the stock may be allowed to cool naturally to a relatively low temperature such as to about 300 to 500 Fahrenheit before the coolant is applied. It has also been found the stock can even be allowed to cool to room temperature. The jet 52 or 52 may then direct a hot fluid such as hot water or steam against the surface to produce the desired thermal flow. Accordingly, the foregoing disclosure and description thereof are for illustrative purposes only and do not in any way limit the invention which is defined only by the claims which follow.

What is claimed is:

1. A nondestructive tester for inspecting flat stock while the temperature of said stock is changing, said tester including the combination of a radiometer for receiving infrared radiations from a surface of said stock and producing an electrical signal that is a function of the radiations,

means for focusing the radiometer on successive discrete areas of the surface of said stock whereby the signal is a function of the temperature of said areas, and

utilizing means coupled to said radiometer and responsive to said electrical signal therefrom, said utilizing means being effective to perform an operation whenever the temperature differential between said succes sive discrete areas on said stock varies beyond a predetermined limit.

2. The combination of claim 1 wherein the utilizing means includes an indicator which is effective to indicate abnormal variations in the surface temperature of the particular area.

3. The combination of claim 1 including means for scanning the plate with the radiometer whereby said particular area follows a scan line on said surface and said electrical signal corresponds to the surface temperature along the scan line.

4. The combination of claim 3 including means for varying the temperature of at least a portion of the plate whereby the particular area has cooled for a predetermined time interval before the radiometer receives the radiations therefrom.

5. The combination of claim 4 wherein said means includes a jet for directing a stream of coolant against a surface of the plate.

6. The combination of claim 5 wherein said jet is disposed on the opposite side of the plate from the radiometer whereby the plate is cooled on one side and scanned on the other.

7. In a hot rolling mill for rolling plates the combination of a set of rollers of rolling a plate while said plate is hot,

a rolling table adjacent to the rollers for receiving the plate after it has been rolled by the rollers and while it is still at an elevated temperature,

a temperature sensor disposed near the rolling table and spaced from a plate thereon, said sensor being effective to measure the surface temperature of portions of plate carried on the rolling table, and

means coupled to the temperature sensor and effective to indicate when the temperature differential between portions of the surface of the plate varies beyond a predetermined level.

8. In a device of the class described the combination of a rolling station for holling hot steel plates,

a trimming station for trimming the hot plates after they have been rolled,

a rolling table disposed adjacent to the rolling station for receiving the plates while they are being rolled by the rolling station for transferring them to the trimming station after the completion of the rolling operation, and

an inspection station disposed adjacent the rolling table between the rolling and trimming station, said inspection station including means to measure the temperature of a portion of the surface of the hot plate and to indicate when the temperature differ ential between said portions varies beyond a predetermined limit.

9. The combination of claim 8 wherein the inspection station includes a radiometer positioned adjacent the rolling table and spaced from a plate thereon, said radiometer being effective to receive infrared radiations from the surface of said plate and produce an electrical signal that is a function of the temperature of said surface, and

means responsive to said electrical signal and effective to indicate where there is a defect in the plate.

10. The combination of claim 8 wherein the inspection station includes means for directing a stream of coolant onto said hot plate as said plate travels along the rolling table whereby thermal energy is absorbed from the plate.

11. The combination of claim 10 wherein the inspection station includes a radiometer positioned adjacent the rolling table and spaced from a plate thereon,

means for focusing the radiometer onto an incremental area of the plate whereby the radiometer receives infrared radiations from the incremental area and produces an electrical signal that is a function of the temperature of said area.

said cooling means being disposed anterior to the incre mental area whereby said signal is a function of the temperature of the incremental area after the plate has been cooled for a predetermined time.

12. The combination of claim 11 wherein the inspection station includes means responsive to the temperature signal and eifective to indicate when the temperature varies abnormally.

References Cited UNITED STATES PATENTS 2,933,956 4/1960 Snow 72l3 3,043,956 7/1962 Cohen 25083.3 3,044,297 7/1962 Hanken 73-355 3,174,316 3/1965 Sigal 72203 3,188,256 6/1965 Shoemaker 25083.3 3,267,709 8/1966 OBrien 72l3 3,290,913 12/1966 Wilson 72l2 OTHER REFERENCES The Iron Age, Infrared Scans for Inner Defects, Malin, May 27, 1965.

Milleton, Inc., Bulletin No. REl. Rockwell Manufacturing Co., Bulletin Model 9240.

MILTON S. MEHR, Primary Examiner US. Cl. X.R. 25083.3 

